linux-ext4 - [Bug 15792] ext4_inode_inode->i

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Message-Id: <201004152252.o3FMqTdl006732@demeter.kernel.org>
Date:	Thu, 15 Apr 2010 22:52:29 GMT
From:	bugzilla-daemon@...zilla.kernel.org
To:	linux-ext4@...r.kernel.org
Subject: [Bug 15792] ext4_inode_inode->i_flags modification is racy

https://bugzilla.kernel.org/show_bug.cgi?id=15792





--- Comment #4 from Dmitry Monakhov <dmonakhov@...nvz.org>  2010-04-15 22:52:22 ---
Most interesting part is last lines

[61] [2]   truncate clr s:737987 d:737987 b:104 fl:80000 
[62] [0]   clr ext4_inode_blocks_set b:104 fl:480000 bit:40000 
[63] [2]   trunc_ext begin s:737987 d:737987 b:104 fl:480000 ml:1 

I.E.
CPU2: is doing  EXT4_I(inode)->i_flags &= ~EXT4_EOFBLOCKS_FL
CPU0: is doung  ei->i_flags &= ~EXT4_HUGE_FILE_FL
CPU2: Wow  EXT4_EOFBLOCKS_FL appear again due to race with cpu0.
So even if truncate holds i_mutex it is possible to modify i_flags.
Seems that we have to modify i_flags via anomic bits operations.

A fix is almost ready. Currently i'm testing it.

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